Contents 7 ARCING DEVICES 101 Mosdorfer GmbH. 8160 Weiz, Austria. Phone +43 3172 2505-0, [email protected], www.mosdorfer.com Subject to change without notice Upper arcing horn for disc insulators, single .............................................................. 107 Lower arcing horn for disc insulators, single .............................................................. 107 Upper arcing horn for disc insulators, double ............................................................. 108 Lower arcing horn for disc insulators, double ............................................................. 108 Upper single path arcing ring for disc insulators .......................................................... 109 Lower single path arcing ring for disc insulators .......................................................... 109 Lower single path arcing ring for disc insulators, with ball ................................................ 110 Lower single path arcing ring for disc insulators, tube material, with ball .................................. 110 Single path arcing ring for longrod insulators ............................................................. 111 Single path arcing ring for longrod insulators, with ball ................................................... 111 Single path intermediate arcing ring for longrod insulators ............................................... 112 Lower single path arcing ring for longrod insulators, tube material, with ball ............................. 112 Grading ring for composite insulators, tube material, with clamp xing ................................... 113 Fork type arcing ring for longrod insulators ............................................................... 113 Fork type intermediate arcing ring for longrod insulators ................................................. 114 Fork type arcing ring for longrod insulators, with ball ..................................................... 114 Fork type arcing ring for longrod and composite insulators, tube material, with ball ...................... 115 Bundles arcing ring for composite insulators .............................................................. 115 Single arcing ring racket type tube material ............................................................... 116 Double arcing ring racket type tube material .............................................................. 116 Single arcing ring racket type ............................................................................ 117 Double arcing ring racket type solid material ............................................................. 117
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7 ARCING DEVICES
101
Mosdorfer GmbH. 8160 Weiz, Austria. Phone +43 3172 2505-0, of�[email protected], www.mosdorfer.com Subject to change without notice
- Even distribution of the electrical field along the insulator string, suppressing partial discharges and corona effects. To achieve this control, the design, shape, size and positioning are optimi-sed to shield tension and suspension clamps. For higher levels of electrical stress control, special corona rings guarantee suppressi-on within required limits.
- Protecting the insulator from the effects of a power arc requires that the device must absorb the full effect of the power arc, acting as a sacrificial component to avoid insulator damage.The device design takes and controls an instantaneous high energy power arc flashover, that has sacrificial parts specifically positioned that may partially burn away to protect the insulator. These events may be triggered by insulator pollution during overvoltage surges.Once the arcing device has collected the root of the arc, the fitting passes energy between the sacrifiacial burning points instantaniuosly. The position relative to the insulator is important, and must be large enough to protect the insulator from the extreme high tem-perature and radiated heat.To ensure the burn flash over point stabilises the arc to burn one point, the power must be fed unidirectionally, and allow electro-magnetic forces to act upon the power arc. Where replacement of arcing devices become necessary, open rings will allow easy installation, and create migration to the intended burn point. Design of the open ring ends must also avoid corona discharge.
The installation arrangement of arcing devicesThe installation of arcing devices will always need adaption to meet performance requirements. The tower support structure and shape, including the insulator string design affects the design of the installation. Where the design is correct, power arc direction will avoid the insulator. Where the power arc direction close to the conductor is unavoidable, special attention needs to be made regarding the design of the end fittings. This ensures that power arc enrgy is directed away from the conductors, avoiding possible conductor damage.
Arcing devices must not restr ict i n su la to r s t r ing movement o r articulation caused by normal wind energy movement.I f necessar y, connect ing a rms are shaped to provide necessary clearances, and ensure that arc gaps are maintained during normal wind induced movement.
General
Arrangement ofarcing devices in case of a double
suspension string
Lower one-way arcing ring with a long rod insulator
Bundle ring with a composite insulator after a rollover test
Arcing device for big displacement
angles (left)and
Arcing device for an arrangement in
conductor direction (right)
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Mosdorfer GmbH. 8160 Weiz, Austria. Phone +43 3172 2505-0, of�[email protected], www.mosdorfer.com Subject to change without notice
Short circuit capabilityShort circuit capability of arcing devices depends on the cross section through which the current flows. As arcing devices are not mechanically loaded, a power density of 80 A/mm2 is required. This value guarantees a temperature rise is limited to 490°C, as accepted by German DIN requirements. Intermedi-ate arcing rings for long rod insulators can be made smaller, as the initial power surge will be combined for short durations.
The materials used for fork type arcing rings can also be smaller, as the stress is shared by two half pieces.
StandardsTest qualification of corona resistance acc. to EN 61284 (Overhead lines - Requirements and tests for fittings) including power arc test requirements acc. to IEC 61467 (Insulators for overhead lines - Insulator strings and sets for lines with a nominal voltage greater than 1000 V - AC power arc tests) are both made on complete insulator strings.
The values required for corona extinction voltage are partly stan-dardized in national Standards. Test configurations are described in EN 61284, where results can be verified. Testing arrangements, including system calibration, test current, number and duration of short circuit currents, are all de-scribed in IEC 61467.
Connection interface dimensions for arcing devices are made acc. toDIN 48068 (Protective fitting attachment; for overhead lines, connection dimensions)
For 24 mm ball fittings, arcing devices are fixed with 2 screws M14 at 32 mm centres, to withstand short circuit currents that may occur.
Double screw fixing are also possible acc. to Swiss and Italian Standards (see Part 3 of the catalogue).
Arcing devices of the “racket” type will be fixed to the yokes by using two screws M 14 at 60 mm centres.
Corona rings are fixed individually depending on possibilities within the string design.
Cascadedpower arcs areunited to one overall power arc
Mosdorfer GmbH. 8160 Weiz, Austria. Phone +43 3172 2505-0, of�[email protected], www.mosdorfer.com Subject to change without notice
Closed arcing ringsFor compact lines, distances are smaller which can lead to corona discharge problems.
During short circuit events, nowadays transmission lines will be switched out rapidly. Therefore the ef-fects of power arc faults will be limited. This creates the possibility to use closed rings, and provide incre-ased corona voltage extinction performance.
Composite insulators normally require a corona ring on both ends in order to avoid electrical field stress at the material transition points of the end fittings.
This also helps to prevent occurrence of partial discharges and co-rona phenomena, which can lead to insulating material degradation of the composite insulators.
In many cases, it is useful to install an arcing ring in addition to the corona ring, as corona rings generally do not support arcing protection requirements.
The corona ring will be connected to the insulator on the end fitting by a suitable clamping device.
Closed rings are also used as corona rings forshielding suspension clamps and tension clamps oncase of ultra-high-voltage lines.
The designs of the rings are dependent on the system voltage and performance requirements, and are ad-apted to meet specific requirements.
Closed arcing ring
Example fora computation
of fields(Lapp Insulators)
Tension string with arcing rings
Corona ring and arcing device
- Unless otherwise specified, all ferrous components are hot dipped galvanized acc. to EN 61284 or ISO EN 1461; Overhead lines-requirements and tests for fittings. Where stainless steel fasteners are used, ISO EN 3506; Mechanical properties of corrosi-on resistant stainless steel fasteners - Part 1: Bolts, screws and studs are specified.
- For lines constructed in higher corrosive atmo-spheres and environments, the minimum zinc thickness of fittings can be increased from 85 μm to 110 μm or 130 μm Microns.
- All fitting assemblies supplied have identification marking according to EN 61284; this includes manufactures mark, date code and 1 second short circuit current withstand rating.
- Where short circuit currents are very high, it is possible to provide a power by-pass using a shunt. Connection facilities are provided at the attachment points.
Material
Shunt connection for high short
circuit currents
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Mosdorfer GmbH. 8160 Weiz, Austria. Phone +43 3172 2505-0, of�[email protected], www.mosdorfer.com Subject to change without notice
Arcing rings for insulated crossarmsInsulated cross arms are used for compact lines, and made up of many different types of insulating materials, or combinations of glass, ceramic and composite insulators. The tensile insulators often consist of two parallel strings combined with one compression load bearing insulator, where the cross arm is made of porcelain or com-posite materials. For these applications, specific designs of combined arcing devises and corona rings are required.
Combinations of arcing ringsFor double and triple strings sets, live string distances should be as small as possible for safety reasons. Arcing devices should have burn points as far as pos-sible away from the insulators, where it is sometimes not practical to utilise two identical arcing devices. For long rod porcelain insulators, it is also important to ensure arcing rings cannot cause damage to re-maining support strings, where load transposition failure has occurred.
Arcing rings for UHV (ultra-high voltage) and DC (direct current) linesFor very high voltages and DC lines >500kV, arcing devices listed in the tables may not be suitable in terms of corona resistance. These arcing devices utilise tube diameter ≤60mm. For all other parts, larger fittings for very high voltages and mechanical loadings will be required.
Buldle ringsThe material used to manufacture the bundle ring guarantees rapid transmission of short circuit current, with excellent corona behavi-our. These rings can also be used on composite insulated cross arms, where they reduce electrical field stress, and act as arcing device protection.
Bundle ring
Arcing ring forinsulated crossarms
Combination of arcing rings for double suspension strings
Arcing rings for UHV lines
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Mosdorfer GmbH. 8160 Weiz, Austria. Phone +43 3172 2505-0, of�[email protected], www.mosdorfer.com Subject to change without notice
Arcing rings for rigid V-stringsThe end of rigid V-strings will be connected to yoke plates at the live side, with a single arcing device at-tached. This will act to protect both insulator strings, and should be designed according to the one-way principle, of leading the power arc away from the insulator.
Adjustable arcing devicesIn order to protect the equipment of substations, nominal gaps can be adjusted on the towers close to the substation. This is achieved by use of adjusting arcing devices that can provide arc gap adjust-ment. Double insulator strings only require arcing protection devices attaching to one string.
For longer insulators, for example in polluted environments, arcing devices are available to offer the correct level of protection for all insulation creepage length requirements.
Corona rings for supporting insulators and devicesOpen and closed aluminium rings for shielding in different tube thicknesses and ring diameters are available.
Arcing rings for rigid V-strings
Adjustableprotective horn
Corona ringfor post
insulators
Tension string with cap and pin type
insulators with long arcing devices
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Mosdorfer GmbH. 8160 Weiz, Austria. Phone +43 3172 2505-0, of�[email protected], www.mosdorfer.com Subject to change without notice